export class DataTableExportDemo implements OnInit {

    cars: Car[];
    
    selectedCars: Car[];

    constructor(private carService: CarService) { }

    ngOnInit() {
        this.carService.getCarsSmall().then(cars => this.cars = cars);
    }

}

<p-dataTable #dt [value]="cars" exportFilename="cars" [(selection)]="selectedCars" selectionMode="multiple" [metaKeySelection]="false">
    <p-header>
        <div class="ui-helper-clearfix">
            <button type="button" pButton icon="fa-file-o" iconPos="left" label="All Data" (click)="dt.exportCSV()" style="float:left"></button>
            <button type="button" pButton icon="fa-file" iconPos="left" label="Selection Only" (click)="dt.exportCSV({selectionOnly:true})" style="float:right"></button>
        </div>
    </p-header>
    <p-column field="vin" header="Vin"></p-column>
    <p-column field="year" header="Year"></p-column>
    <p-column field="brand" header="Brand"></p-column>
    <p-column field="color" header="Color"></p-column>
</p-dataTable>